The tenancy disputes which occurred in the countryside of Japan after World War I had a clear-cut regional character. In the 1920's, disputes were concentrated in the regions of western Japan, with the execption of the South-Kyushu region. There were fewer disputes in the regions of eastern Japan, with the exception of the South-Kanto region. Although there have been many attempts to interpret this regional character, nobody has factored in the regional character of birth rates in pre-war Japan. The aim of this paper is to examine the relationship between birth rates and the agricultural structure of each of these regions, and to consider the regional character of birth rates as a contributing factor in the regional character of tenancy disputes around 1920 in Japan. The followings are main findings regarding regional birth rates, agricultural structure and tenancy disputes: 1) The birth rate in eastern Japan (outside the South-Kanto) was higher than the national average during the pre-war period, while that in western Japan (outside South-Kyushu) was not only lower than the national average, but also started to decrease after 1910; 2) The number of farm households in the Tohoku and North-Kanto regions in eastern Japan and in the South-Kyusyu regions, where the birth rates were especially high, increased steadily. On the other hand, the number of farm households in the Chubu, Kinki, Chugoku, and Shikoku regions of western Japan decreased steadily during the inter-war period; 3) During the recession which followed World War I, many tenant farmers returned their land to landowners in the Chubu and Kinki regions because of the low-profitability brought on by the low market price of rice. This triggered the tenancy disputes in these regions; 4) These tenancy disputes spread to western Japan (outside South-Kyushu), where the number of farm households had decreased and bargaining power had shifted from the landowners to the tenant farmers; 5) Tenancy disputes were fewer in eastern Japan (outside the South-Kanto), where the number of farm household was still increasing and landowners could held bargaining power against tenant farmers.